Motors and motor control systems for controlling the motors are widely applied as means to convert electric power into mechanical output, to fans, pumps, compressors, automobiles, railroads, for example. On the other hand, as a problem of the motor control system, a step-out caused by a sudden load torque (instability of motor speed and torque), vibration caused by pulsation load torque, and the like are known. As techniques for detecting and preventing these problems, there are PTLs 1 and 2.
In PTL 1, in order to detect the step-out caused by the sudden load, a motor current is Fourier-analyzed and its pulsating component is compared with a reference value. If a step-out occurs due to the sudden load torque, since the pulsating component of the motor current exceeds the reference value, it is possible to detect the step-out. Furthermore, by transmitting information on the loss of synchronization detection to a host controller, safety can be improved.
PTL 2 reduces vibrations due to the pulsation load torques. A rotor position is estimated from the motor current, and the pulsation load torque is estimated by substituting the position estimation value into the motion equation. Next, Fourier analysis is performed on the pulsation load torque, and the output voltage of the inverter is pulsed so as to cancel each frequency component. If the pulsation amount of the output voltage is appropriate, the motor torque and the pulsation load torque cancel each other out and the vibration is reduced.